text:
How to calculate the heading correction with a circular flight computer?
While flying between 2 points 120 nautical miles apart, after about 40 nautical miles we discover we are 5 nautical miles off to the right of the track.

What heading correction is necessary in order to reach the destination? How do you calculate the correction using a circular flight computer?

1 - First I calculate the track deviation angle:
To find the track angle:
outer scale: distance off track (NM) in this case 5 NM
divided by
inner scale: distance already travelled(NM) in this case 40 NM
To do this I divide 5NM per 40NM as per the picture below, the division is within the red circle and the result is pointed by the red triangle that says '60' on the other red circle with the arrow pointing to it.
the result is 7.5 as you can see on the picture below.

2 - Then I calculate the closing angle for the remainder of the journer:
To find the closing angle:
outer scale: distance off track (NM) in this case 5 NM
divided by
inner scale: distance to go (NM) in this case 80 NM
The remainder of the journey is (120NM - 40NM) = 80NM
The current deviation which is 5 NM.
To do this I divide 5NM per 80NM as per the picture below, the division is within the red circle and the result is pointed by the red triangle that says '60' on the other red circle with the arrow pointing to it.
the result is 3.77 rounded down to 3.7 as you can see on the picture below.

3 - Then I calculate the total heading correction:
total heading correction to reach the destination = track error + closing angle
that is:
7.7 + 3.7 = 11.2 degrees
so the heading must be corrected to 11.2 degrees left.

The true angles (based on using trigonometric functions on a digital calculator) are ≈ 7.18, 3.56, and 10.74 degrees. The first angle is asin(5/40). My guess is that 60 is used as an approximation for 180/π ≈ 57.3, and I'm surprised that the calculator doesn't have an arrow at this point. If it had your results would be 7.2, 3.6, and 10.8. EDIT: Wikipedia points this out, along with the fact that it's not possible to fly manually with enough accuracy for it to matter.


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Why isn't there a procedure for dual-engine failure in twin-engine airplanes?
I'm licensed to fly multi-engine aircraft. I currently fly the DA-42NG.
However, nowhere in my training and in the official POH was I introduced to procedures for handing a dual-engine failure in-flight.
There's no mention of a Best Glide Speed whatsoever.
I'm assuming this is the case for most, or maybe all GA Twin-Engine airplanes. I know jets can glide for some time without any power.
Question is - can GA airplanes? I know it won't fall like a rock - but there's got to be some science to follow here, right? Why haven't the manufactures mentioned it even once? Why isn't it part of the training?

Usually for light singles, glide speed is pretty much the same as approach speed, which is 1.3 * VSO. I can't imagine with feathered props that this rule would be much different in twins, so if you have a dual failure scenario I'd stick to normal approach speed as your glide speed. The other advantage is you should be very familiar with that descent rate and distance.

My opinion on the subject is that the powers that be, over aviation, evolved from a single-engine transitioning to multi-engine mindset, and therefore, it is ingrained in the training culture that anyone who is earning a multi-engine rating posesses a single-engine rating, and that, in the case of all engines failing in a multi-engine airplane, they would utilize the training for an engine failure in a single-engine airplane.  Due to that, multi-engine curriculum exclude this.

I can't understand why there is already a close vote on that question. If the voter could explain...

@RyanMortensen Granted that is true, the aircraft manual should still list a best glide speed.

I wonder if maybe it's a safety issue to list a best glide speed.  What if both engines fail, someone goes to best glide below Vmca and then for some reason, an engine restarts and puts the plane in a spin.  That's probably not the reason, but then again... lawyers.

I'm guessing that it must be certification requirements.  Transport category aircraft (at least all of the two and three engine models that I have flown) DO have an "all engines out" emergency checklist procedure.

The best endurance glide speed is (for all aircraft) the same (or nearly so; the propeller drag might make a small difference) as the best rate of climb speed. Best distance glide speed is a bit higher (while best angle of climb is a bit lower).

@RyanMortensen I'm not sure I fully agree. While we of course hold a single-engine certificate before getting a multi-engine rating, how we handle engine failures in single engine vs multi-engine is not exactly the same. Regardless - it is unlikely that the licensing authority would simply want pilots to "do what you learnt when flying the SE aircraft".

@RaajTram well for one thing, there is no rule, at least not in the U.S., that says you can't be multi-engine rated without being single-engine rated, but I have yet to meet anyone who only has M.E..  I'm not asserting anything with certainty here, which is why I haven't posted an answer, just comments.  Manufacturers may exclude it because going below Vmca (down to best glide) is considered dangerous in case one engine restarts itself (just a guess).  I don't see how procedures for a multi-engine-all-failed, scenario would be much different than the procedures in a single-engine.

Have you read all the manuals? Jets usually have table somewhere for speed to fly without engines. Anyway the speed will be near the best rate of climb speed. On Airbus 320 is green dot speed.

There are.  The Metroliner (SA227) has a dual flameout checklist.  It's possible that the company I flew for developed their own and had it approved, but we DID have a checklist for that.
I think they're rare on pistons twins because there are a very limited number of environmental factors that can cause double engine failures.  It's also possible to simply run out of gas.*  A turbine can ingest water, ice, dust, sand, snow, etc (no filters) that can contribute to a flameout.  The factor that causes one to quit will likely effect the other in a similar way.
I do know a pilot who flamed out both engines by using engine inlet heat on both engines at the same time.  The ice melted off the inlets at about the same time, both engines ingested the ice, and they quit.  He managed to relight both of them and landed uneventfully.  That likely would not happen in a piston twin.  The alt air doors would open and keep the engines running.
*If you find yourself thinking "I'm going to need that double engine failure checklist in about 20mins," you should probably seriously reflect upon the decisions you made throughout the flight.

Fuel starvation is pretty common in GA and would certainly effect both engines.

Right, but that is generally a pilot controlled problem. My understanding is that the double engine failure checklist is there to cover unforeseen external causes of engine failures. I can't explain how I got that idea into my head...must have been part of some training along the way. I agree with you though, running out of gas another reason for a double engine failure.

Yeah, but Greg is right.  Engine failures due to pilot error are still engine failures, and we should expect procedures to exist,.

I can't argue with that.

@acpilot expecting an engine failure (dual or single) vs experiencing an engine failure all of a sudden are two completely different scenarios. The former is undoubtedly the pilot's fault, but not the latter. My original question is related to the latter situation.

It still cold be the pilot's fault.  See engine ice example in the answer.  I can think of few instances of sudden double engie failure in which the pilot would not be somehow responsible.

Training is done to the extent that there are procedures to follow for a particular failure.
There are checklists for restarting engines during a dual engine failure, but the checklists don't include what to do if they can't manage to restart to engine.
They must use their knowledge and piloting skills to glide to a nearby airport.

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text:
What is the descent rate in emergency situations?
I fly a plane at 40000 feet. There is a sudden depressurization; what is the maximum vertical speed I can keep to come back at a proper altitude?
Is this speed different for different emergency situations? (Engine stopping/fire/general emergency).
Are there any numerical maximum values in different scenarios for, for example, a A320 or a B737?

Several thousand feet per minute.  It is not possible to provide a precise answer to your question with the information provided.

Your edit of the question now makes my answer seem out of place.

Get as much drag out as permissible: spoilers, gear, etc. and descend as fast as you can.  Mmo / Vmo.  Most airplanes will get down in around 4 minutes to 10,000 FT MSL from their maximum operating altitude.

@SentryRaven My question is "which is the speed"? So, I want a numerical value in some possible situations. And since I understand it may be too broad, I ask for a specific value of a generic airplane, for example A320 or B737. Why shouldn't be a legitimate question?

Your initial question asked " Is this speed different for different emergency situations? ". My answer was based on that. I'll let someone else answer this, you are changing your question every few seconds and I cant keep up with that.

@SentryRaven My initial question, as you can also see from the chronology, was "which is the speed". My edits were done because you asked for clarification and then changed the question in order to let it fit with your answer. Let someone else answer this. It's okay. Thank you anyway.

Are you asking for the speed as shown on the VSI (Vertical speed indicator) which is a rate of descent indication, or an airspeed/mach number to fly while descending without exceeding structural limits of the aircraft/wing?

In 747-100/200 aircraft, after you got the gear out, you kept the nose down to whatever angle was required to maintain mach .82 and then 320 kts IAS and accepted whatever descent rate that produced. I never bothered in the sim to monitor what the rate of descent was since that wasn't a controlling factor, but I think it pegged out the meter, which stopped at 6000 fpm.

In a rapid depressurization, you'd typically descend at MMO and transition to VMO until reaching your level-off altitude. This is accomplished with the speedbrakes extended. What vertical speed you'd get is unknown; essentially you take whatever rate this procedure gives you. Initially, it might be 6000+ FPM, after transition to VMO, maybe a little less than that.
But, you set an airspeed, rather than a vertical speed.
Edit:

MMO = maximum Mach Number (often, .82 or above, depending on aircraft type)
VMO = maximum Indicated Airspeed (often around 340 knots)

The vertical speed is your horizontal speed divided by the actual L/D at the given speed and configuration. With spoilers out this should be less than 10. Details depend on the type of aircraft.

The Mesa E175 that had an emergency descent about a year ago peaked around 7000 fpm, in total taking 6 minutes to descend from FL340 to 10,000 ft.

(flightaware.com)
In light of the comments above about MMO/VMO and lift/drag limiting descent rates, you can accelerate descents by banking the aircraft into a turn. This allows you to increase angle of attack, thus increasing drag to keep speeds down, while rotating the lift vector away from the vertical so it's not working against you. The combination allows for higher descent rates with the same MMO/VMO limits. Some operators train for this, but my impression is not many, and it tends to scare the passengers.

Neat information and graph!!!

I can't answer for to 40,000 feet (FL400—Flight Level 400—in pilot parlance), nor to an A320 or B737. I can answer for a piston engine airplane with retractable landing gear at FL250, though.
As a private pilot, I frequently fly our Mooney 252 (M20K) at FL250. I did an emergency descent drill, running through the procedures to initiate a maximum-rate safe descent, something I would do if I had a fire in the airplane or an oxygen emergency. (The 252 is not pressurized: I have supplemental oxygen on board, delivered to my face using an oxygen mask.)
The procedure: power to idle, speed brakes deployed, landing gear extended ("down"), 160 KIAS (knots indicated airspeed), propeller control full forward (increases drag). The 252's maximum speed with gear down is 165 KIAS, and I want that little bit of extra margin. My vertical descent rate exceeded 5,000 feet per minute.
There are other scenarios, though, for "emergency descents": you might want to go as far along the ground as possible (engine failure, glide to a distant airport for landing), when you want to fly at the best glide speed (compensated for wind and for actual airplane weight, ideally); you might want to stay aloft as long as possible (engine failure right over an airport, and you want the time to attempt a restart or to prepare more thoroughly for the landing), so you'll fly at the best sink speed. In my airplane, best glide is at about 85 KIAS, best sink is about 75 KIAS.

you can probably increase that 5000fpm to 7000 or more if you put a boot full of left rudder and opposite aileron to slip the a/c. The noise will be horible at 160kts though if you survive it will probably be a fun story to tell

Interesting thought, @Radu0904: add a slip to the maneuver. I don't know that the noise would be so horrible. I have used slips to lose altitude quickly on final when needed (airplane without flaps, or when all the drag on the Mooney is already deployed), and the noise isn't at all horrible—but, that's at about 80 KIAS, not 160 KIAS. Next time I'm up doing some emergency descent drills, I might add this and see what the descent rate is.

The best configuration and technique depends on the airplane. In a Navion I owned, I could only get about 1200fpm using flaps and gear at Vfe (max flap speed) . I was better off (2000fpm) staying clean and side slipping at top of green Vno (normal operating speed).

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How can you identify an Airbus and or Boeing from the inside based on features of the interior?
I already asked a very similar question, but the answer wasn't was I was expecting. Hence this time I am more specific.
How can you recognize a plane from the inside, when you are already sitting as passenger?
In particular, is there a way to understand if you are inside a Boeing or an Airbus based on interior features of the aircraft?
The question is specifically related to the differences in interior features between aircraft built by the two companies. I am not looking for answers such as "check on your ticket", "ask the flight attendant" or "read the evacuation pamphlet".

Possible duplicate of How can you identify an Airbus or Boeing from the inside?

Please clarify your original question instead of asking the exact same one again. Also, what is the meaning of the word "Vel"? Google tells me it's the spear of a Hindu war god, but I don't think that's the meaning you're after here.

@Freeman He tried  to clarify his original question, but that was rolled back. See the associated Meta discussion.

@DeltaLima, your point is very valid. However, your edit to this question seems like it would fit perfectly well on the original question, as well. My opinion has been expressed, as has yours and others. I'll not argue any further, it's not that big a deal.

This question is a little bit broad, you might consider asking how to tell the difference between particular planes that would be hard to differentiate by obvious means.  For example, maybe asking how to tell the difference between a 737 and an A320 simply by the interior?

Well, the overhead bins and ceiling are quite aircraft specific, but then you need to be quite an expert to be successful in identifying an aircraft that way.
Then there is the shape of the fuselage, an A380 for example has a large radius fuselage so if you're on the lower deck the curvature of the fuselage is very low and almost straight.
A Dreamliner has very distinct windows.
An airbus has a different lightning array in the roof compared to a Boeing.
As you can see this list can go on and on depending on how skilled you are in spotting the differences between interior layouts. If you count the seats abreast you can already skip a lot of planes since they typically have 6 seats abreast or between 10 and 12 etc. Some aircraft have a widebody etc.
As a passenger the easiest way is to look at the evacuation map or look at the moving map in the IFE system.

Not sure if the info is available, but if indeed there is a consistent difference between airbus and boeing overhead bins and lighting, you may be able to answer this question definitively by showing some reference pictures.

Did you mean "lighting array" or perhaps even "lightening array" rather than lightning?


text:
How do we choose a frequency range of interest for flutter prediction?
I'm trying to perform some flutter and dynamical (gust etc.) calculations with Nastran. It has been told to use a range up to 30 Hz for an aircraft I'm working with, but why the upper limit is so choosen 30 Hz? Why for some aircraft the range is up 60 Hz and for another one even up to 100 Hz? I suppose it depends on matirials used in a particular structure and/or a frequency range of presumed loads. I would be grateful if someone can explain how the frequency range of interest is exactly chosen. Thanks!

You might want to try reviewing MIL-A-8870C  AIRPLANE STRENGTH AND RIGIDITY
VIBRATION, FLUTTER, AND DIVERGENCE.  The CRJs were certified to this standard.  Available here: http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-A/MIL-A-8870C_6746/  Just click the Download File button.

Why would civilian aircraft be certified to military standards?

Yes MIL-SPEC, MIL-PERF and Standards are used across the industry for all sorts of things in the civilian world of aerospace, because traditionally there was always a lot of overlap.  Why reinvent the wheel?  The old AN standard for aircraft hardware stands for Army/Navy. In the case of MIL-A-8870C, a manufacturer may choose to develop their own analysis for flutter margins, but they can also just use 8870 if they want.

Ah, I always imagined MIL SPEC to be very different requirements (i.e. more or less stringent) than the commercial ones.

One interesting change in the aerospace industry was a gradual switch from MIL-SPEC to MIL-PERF.  MIL-SPEC components are built to a specific physical specification.  Under MIL-PERF, a component only has to meet a performance standard.  This allows commercial non-aerospace components to be used as long as they meet the PERF standard in performance.  Example: around the turn of the century microprocessor makers stopped producing processors made to the old MIL-SPEC.  Manufacturers started to use commercial components, allowable as long as they met MIL-PERF requirements.

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text:
Will two blades or three blades last longer on a hobby drone?
Will it be better to run a lighter 2 blade prop vs a heavier 3 blade prop for longevity and battery life? they are the same length. I am curious if the extra weight of the third blade will inhibit the time..

I have edited your question to make it more readable.  If this has changed the meaning feel free to roll back to the previous version.

A 2-blade prop should be better. Read here about the efficiency of props and their blade count.


text:
What is the difference between ground speed and airspeed?
What is difference between ground speed and airspeed? Is ground speed used only for takeoff or is it used for flight too?

Snarky answer: it's literally the magnitude of the component of the wind speed in the direction of travel.

Not a duplicate... the referenced question is asking about a video game, and got an answer with more formulas than a college level Aero course.  This question is asking for a straightforward answer to the concepts of airspeed and groundspeed, and aviation.se doesn't have that -- at least not in the referenced "duplicate" question. Voting to reopen.

You are headed east at an indicated 100mph, the air mass you are in is headed west at 10mph, your indicated air speed will be 100mph, the ground speed will be 90mph since you have a 10mph head wind. If the air mass were heading east (tail wind) at 10mph, your indicated airspeed would still be 100mph, but your ground speed would increase to 110mph. Make sense?

GPS speed is the same as Ground speed.  The "Flight Simulator" video game question and answers are also applicable to real life so the question has been answered correctly. I vote to remain closed.

The ground speed is the speed the aircraft is making over ground below.
The indicated airspeed (IAS) is the speed shown on the airspeed indicator. This will be different than the ground speed for various reasons, such as wind and the attitude of the aircraft. For example, if the aircraft is diving then the IAS will be greater than the ground speed. In fact, if the aircraft were diving straight down, then the ground speed could be 0 while the IAS was hundreds of knots per hour.
The indicated airspeed is the usual measure used in flight.
The ground speed can be calculated to estimate the time of arrival of the aircraft at some destination.

In my opinion this answer is poorly written. The answer should include information how Indicated airspeed relates to True airspeed and how True airspeed relates to Ground speed. The implication that difference between ground speed and indicated airspeed can be partially due to the aircraft diving is misleading and totally unnecessary.

The question as posed I did not regard as requiring a detailed technical answer and such an answer I think would be more confusing than helpful for him. Getting into calibrated air speed, true airspeed, equivalent airspeed and so on is just overkill here and there are already other answers that cover such things. As for the example, I think it is useful to give a very simple and easy to understand example why IAS can differ from ground speed.

If you want to keep it really simple you could say that ground speed is the speed of the aircraft in relation to the ground, and that airspeed is the speed of the aircraft in relation to the air around it.   The mass of air that the aircraft flies through is usually a moving body in relation to the earth(wind), and that accounts for the difference between ground speed and airspeed .


text:
Does air travel in the same time over the top of the airfoil and along the bottom?
If we assume two particles of air arriving at the leading edge, one flowing over the airfoil, the other under the airfoil. Do they arrive at trailing edge at exactly the same time?

No they don't. See: Nasa, incorrect theory #1

Probably a better answer, contains what @mins is referencing: http://aviation.stackexchange.com/questions/16193/how-do-wings-generate-lift

Also relevant: http://aviation.stackexchange.com/questions/1157/why-is-the-wrong-explanation-of-air-travels-a-longer-distance-and-creates-a-lif

Depends on whether the particle gets into the boundary layer or not. If it does it will be slowed down considerably, depending on how much time it spends there, and how close to the wing surface it gets.


text:
Certification of high voltage to low voltage converters
Does anyone have any experience with certification of high voltage to low voltage power converters designed with COTS DC-DC controllers for eVTOL or MEA applications?
I am interested to know about the process and if its possible to use such COTS controllers and obtain a certification.

DC to DC static converters used in avionics (communication/navigation equipment) are approved against technical specifications in a Technical Standard Order (TSO):

TSO C71 by FAA,
ETSO C71 by EASA.

This TSO details values for elements like regulation rate, ripple, over-voltage, short circuit response, RF emissions, temperature range, etc.
More information (FAA):

TSO authorization
FAA process in Part 21.

In the latter process, 21.603 states:

(a) An applicant for a TSO authorization must apply in the form and manner prescribed by the FAA. The applicant must include the following documents in the application:

(1) A statement of conformance certifying that the applicant has met the requirements of this subpart and that the article concerned meets the applicable TSO that is effective on the date of application for that article.
(2) One copy of the technical data required in the applicable TSO.

After reviewing data required by the TSO, FAA and EASA deliver a Letter of TSO Authorization (TSOA), a model is provided in AC 8150, mentioning:

This is in reply to your letter of {enter date of application} requesting TSO authorization for your {insert type of article}. We accept your statement certifying that your article meets the
requirements of TSO-C {enter applicable TSO number} and that you meet the requirements of Title 14, Code of Federal Regulations (14 CFR) part 21, subpart O.

The FAA TSO C-71 is available on the FAA.gov website

Thanks. C71 refers to input voltages up to 28V only though. Can C71 be used for high voltage inputs like 270V, 540V or 800V?

@SSA: No this TSO only applies to a DC-DC converter used in navigation/communication equipment, not to HVDC converters. Unfortunately I'm not aware of HVDC related regulations.

My understanding is the certification is still done to the TSO, but with a deviation for the voltage level


text:
Is there any anti-ice system on Cessna Citation II?
I was flying a Cessna Citation II on FlightGear FS. There are some ice on the windshield when it climbs to about 15000 ft. Is there any anti-ice system (or de-ice system) on Cessna Citation II? (I do not mean Citation X or Citation Bravo.) How can I control these things? I looked for them everywhere in the cockpit, and I can't find them.

There are six green switches at the bottom left corner of the board, visible on this FlightGear screenshot:

(Source)
Details of this anti-ice section, from actual aircraft:

(Source)
"W/S" is for windshield. You can send hot air onto the windshield surface with the W/S BLEED switch and anti-ice fluid with W/S ALCOHOL.
Someone asked the same question on Flightgear forum.


text:
Connector type and pinout for this surplus flight cap headset?
I picked up a flight cap that is similar to this one. In my search, it seems to be frequently described as a soviet Mig flight cap. No idea when/where it was manufactured, but it looks like it could be fun and goofy to hook comms to while the flight sim sounds go to the regular speakers.

The connector looks like the following:

With the pins numbered from 1-5 clockwise from the notch.
In basic testing, it would appear that pins 1 and 2 are used for a mono signal to both headphones. Pins 4 and 5 appear to be for the microphone but when checking signals with Audacity, the microphone barely transmits anything besides spots of noise when I tap it.
These questions are in the context of a flight simulator usage:

What type connector is this? It's too large for a XS12 or GX12 connector, my GX16 connector hasn't come in yet to check.

Does anyone know how to connect it? Is pin 3 for PTT and, if so, how should it be wired up?

Thank you for your response! I don't think a DIN would work because of the pin placement (they are spread out more than DIN pins are). My GX16 connector came in and it mates, but is loose and the headset connector doesn't have the threads for the gx16 to lock in.
I'll look into building the FET pre-amp, but am still curious what pin 3 could be used for?

I don't have an oscilloscope to measure output voltage but a direct resistance measurement across the mic leads shows ~146ohms with my multimeter. So I'm expecting it's not high impedance. I guess I should check my audacity settings.
The 3rd pin being ground lines up with llama3:8b's explanation, and that LLM says that many times the 3rd pin is left disconnected. So I guess I'll just have to give it a test =)


text:
What is the function of the hole at the rear of the airplane?
What is the function of the hole at the rear of a plane?
I searched online but didn't get a satisfying answer.

there are several hole in a typical airplane. you'll get better answers if you provide a picture.

This one? It's the APU(auxiliary power unit)'s exhaust.
An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion.

The primary purpose of an aircraft APU is to provide power to start
  the main engines. Turbine engines must be accelerated to a high
  rotational speed to provide sufficient air compression for
  self-sustaining operation. Smaller jet engines are usually started by
  an electric motor, while larger engines are usually started by an air
  turbine motor. Before the engines are to be turned, the APU is
  started, generally by a battery or hydraulic accumulator. Once the APU
  is running, it provides power (electric, pneumatic, or hydraulic,
  depending on the design) to start the aircraft's main engines.
https://en.wikipedia.org/wiki/Auxiliary_power_unit


text:
Why does a pilot want to hold a Squawk Code when leaving Class B airspace?
I was listening to liveATC today... Controller clears this guy into the class B for a transition and throws him a code. Some time passes and the pilot has now transitioned the bravo and is leaving the airspace. The conversation goes roughly like this:
ATC: N12345 are you going to want a handoff?
N12345: No sir but we'd like to hold our code
ATC: Okay, N12345 you are leaving my airspace, radar services terminated, squawk VFR, frequency change approved, see ya!
Now, I guess this boils down to two questions:
1) Why would he want to keep his code if he's not being handed off to another controller? What difference does that make?
2) Why did the controller still say to squawk vfr, even if the pilot wanted to keep his code and the controller said that's fine? Didn't the pilot go against an atc order by keeping his code and not squawking 1200?
I'm a sport pilot and have yet to use flight following (nor do I have my class B endorsement), so maybe I'm just missing something due to lack of exposure!

Without knowing more of the context it sounds like the pilot wanted to keep the code for flight following services, but the controller was unable or unwilling to provide them and instructed the pilot to sqauwk VFR (1200).
Keeping a code for future use is generally a no-no as discrete codes are limited in number to each facility and managed nationally. This is due to the octal 4096 transponder having so few available codes. There is actually a National Beacon Code Allocation Plan to divvy up the codes and prevent overlap between facilities:
https://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/1027926

The question says the exact opposite: ATC offered a handoff but the pilot declined it.  Why he wanted to keep the code in that case is not clear, but returning soon seems like a reasonable guess.


text:
Are bigger and / or heavier aircraft more resistant to crosswind compared to smaller / lighter aircraft?
When watching heavy crosswind video compilations, I noticed heavy aircraft like the A380 an B747 have a more stable approach compared to the B737 or A320 where the plane banks left and right on approach more frequently.

A constant crosswind affects all aircraft equally. A crosswind gust will however affect a lighter aircraft more than a heavy one due to lower inertia. The acceleration $a$ felt from the gust is
$$ F = m \times a \;\; \Leftrightarrow \;\; a = \frac{F}{m} $$
where $F$ is the force from the gust and $m$ is the total mass of the aircraft. The force is roughly proportional to the area that the wind sees, which scales with the scale factor squared: $ F \sim s^2 $. The mass however is proportional to the volume, which scales with the scale factor cubed: $ m \sim s^3 $. This results in less sideways acceleration from a wind gust for larger aircraft: $ a \sim s^2 / s^3 = 1 / s $. Therefore, there is less need to correct by sharply banking left or right.
Additionally, larger aircraft react to control inputs from the pilots more slowly (for the same reasons), which also makes them look more stable even when the pilots make sudden control inputs.

A real-life case: https://www.spiegel.de/panorama/london-heathrow-spektakulaere-airbus-landung-waehrend-sturm-dennis-a-3c508c41-344e-4501-955d-98c9266dd9c2?jwsource=em

Forward airspeed also matters, in determining how quickly an aircraft will accelerate in relation to a crosswind gust.  In general, the higher the forward airspeed, the more sideforce a given crosswind gust will generate, and thus the more sideways acceleration.

Links re above comment -- See https://aviation.stackexchange.com/questions/70975/how-to-take-into-account-wind-in-aerodynamic-forces-balance/70978#70978 , https://physics.stackexchange.com/questions/176513/calculating-wind-force-and-drag-force-on-a-falling-object/176515#176515 , https://physics.stackexchange.com/questions/491600/flight-time-of-spherical-bullet-fired-horizontally-versus-dropped-vertically-e/491771#491771

@quietflyer Good Point! This is very relevant when comparing with a much smaller plane like e.g. a C172, but for the aircraft mentioned by the OP, it is actually not really relevant. Both the A320/B737 and the A380/B747 have typical approach speeds of around 140 knots.

This cube-square almost doesn't work for airplanes.


text:
Straight Wings VS Delta Wings, Variable wing with Forward swept capability
What are the Pros and Cons (Advantages and Disadvantages) of a Delta wing and a Straight wing against each other, and if a Variable wing with a capability to become a Forward Swept wing is even possible to create.

Pretty sure this is a dupe, but not finding it...

@FreeMan: Yes, it is a dupe, but of more than one question. Here is the part covering delta wings and here the part covering forward variable sweep.

guys, I'm sorry if you misunderstood, but this is not a dupe(duplicate?), it is just that i am new to this stuff, and i'm curious about wings, again sorry for my poor English grammar/words

No need for apologies. I hope you enjoy the additional answers!

At low speed, the key to reducing "induced drag" is to have a high aspect ratio, that is, you want wings that are long and skinny. Think gliders. Now of course, these are not easy to build, and for entirely practical reasons you might want something that's more square-ish than a glider. That's one of the many engineering trade-offs every aircraft design requires. Check out the svelt wings on this Q400:

Things become more interesting as speed increases.
First, as you enter the transonic area above around 450 mph, a new form of drag begins to form, the so-called "wave drag". The way to reduce this is to make the wing as thin as possible, or to be more specific, have as little curvature on the top and bottom edge. Ultimately you want an almost flat plate.
Now of course, lift is generated by that curvature, so that's a problem. And when you try to reduce that curvature to lower wave drag but still want the same lift, well then you have to make the wing larger front-to-back (think about it) and now your induced drag goes up, and skin friction too in most cases.
So then there's a trick. If you sweep the wing to the rear then the air flowing over it travels across a longer distance. So it thinks the wing is longer front-to-back and has less curvature, and that lowers wave drag. Yet at low speeds, the air smoothly flows over the curves and sees the original wing profile. So you get a thick wing that looks thin. Check out this F-86, notice that the wings are actually pretty thick:

Now as you go supersonic, things change yet again. In this case the drag is minimized by having the least width you can get away with. So for these sorts of designs you want short stubby wings with lots of chord (front-back) and you end up with the F-104.:

Now you have a wing that is absolutely terrible at low speeds, and for that reason, lots of F-104s crashed while the pilots tried to keep up with the plane while landing at redonkulous speeds needed to keep the thing in the air.
Deltas are mostly just swept wings with the inside filled in. If you want to see an example that really illustrates this, look at the English Electric Lightning:

If they filled in that little part, it would be a delta. But there is one trick that you get in a delta you don't get in a swept wing...
At very high angles of attack, with the nose high, the air along the leading edge of the wing can generate a vortex right along the fuselage. If there is a wing under it, this generates lift. Poorly, with lots of drag, but lift. So then you get this little one-trick-pony effect; this will works really well at high speed, but also works OK at really low speeds too. But it only works if the vortex is above actual wing, so the Lightning didn't get all the advantage here.
The problem with deltas are that they are big and heavy, but they also get more room inside for fuel. More trade offs. But then someone came up with a new idea: make a normal swept wing and then add a little bit of delta:

You can even see the vortexes in this image. In this case the little-bit-of-delta is called a "leading edge extension".
Variable wings are simply an attempt to put all of these on a single aircraft. Rotate them forward and you have a nice long skinny wing like the Q400. Rotate them back and you have a really swept wing or even a delta, and at the same time the width is being reduced. So now you can go fast or slow. Just weighs a lot.
Swept forward is basically identical to swept back. This isn't about lift in this case but an attempt to control something called spanwise flow. Check out this MiG-17's wing:

Do you see those metal plates? What happens on a swept wing is that the shape causes some of the air to move sideways. This is a Bad Thing. So these plates grab sideways moving air and redirect it over the wing again. The same thing happens on deltas, check out the notch on the CF-105, same idea:

Now the idea here is that the wind is following the wing's leading edge. So what happens if you sweep it the other way? Well then it follows the wing into the fuselage, and stops. Presto, problem solved and no plates or notches! The problem is that it's really hard to actually make one that doesn't snap apart, which is why it's not common.

Your explanation of wing sweep could be improved (see here for the correct explanation) and vortex lift is a matter of leading edge sweep and can be achieved with a swept wing if sweep and angle of attack are sufficient.

@PeterKämpf - why do you think the explanation you linked to is different than mine?

You claim that the oblique flow angle makes the airfoil appear thinner. But there is more to it. The explanation that only the normal component of flow is affected is better because it is able to explain the 3D flow effects that follow.

The big differences between a delta wing and a straight wing break down into thinking about them in two ways: aspect ratio and sweep.  A delta wing is going to have a small aspect ratio (short and stubby) as well as sweep.  Straight wings can have a small aspect ratio (think F-104) or large aspect ratio (more like a U-2).  Delta wings have high induced drag (not good for slow flight) but have favorable characteristics at high speed (like low wave drag).  Straight wings can be stronger because they can be easier to manufacture (this is quite a generalization).  When you make them high aspect ratio, you get lower induced drag and good high altitude performance but of course there are downsides.  You can have aircraft with swept wings that are not delta wings (B-52) for reasons like manipulating the spanwise flow or keeping the wings out of shockwaves.  You can find a lot of literature on wing design; these are just some highlights.  A couple examples of swing-wing aircraft that transition from straight to highly swept in flight are F-14s and B-1Bs.  The X-39 had a forward sweep (made the aircraft very maneuverable) and it flew successfully but it is difficult to build structure like that to handle loads.


text:
Pitching moment due to control surface deflection
How can you predict the change in lift and pitching moment produced by control surface at a certain deflection angle?
I am aware that the effectiveness of the control surface is affected by compressibility. At subsonic speed the contribution to the change in lift force will be higher, but at supersonic speed it decreases significantly. How will the pitching moment change due to deflection of the control surface in either case?

Sections 6.1.1 and 6.1.2 of this USAF DATCOM should answer your question in a very good and simple way.

@sophit mentions DATCOM -- it is a good start.
In general, how are you predicting aerodynamic forces and moments in the first place?  We generally predict control surface contributions to forces and moments using the same tools and techniques.
This can be as simple as thin airfoil theory -- there are tools based on thin airfoil theory to predict the effect of a plain flap deflection.


text:
Minor taking written exam
Does anyone know if a parent/guardian needs to be present for any reason in order for a 16 year old to take the FAA written exam? Or are there any other technicalities/considerations when it comes to a minor taking the written exam?
It seems like the answer is "No", but I'm just making sure...
Thanks


text:
How to call Leidos FSS from Alaskan phone number
My cell phone has an Alaskan area code (907).  When I call 1-800-wxbrief, the automated voice says that I have reached the "Juneau Flight Service Station," even when I am located in Florida.
Has anyone encountered this?  Does anyone know of a way to tell it to direct me to the proper FSS for my location (regardless of my phone number)?

I would suggest staying on the call until someone at Juneau FSS answers, and then asking them if they know of a direct number for Leidos FSS.

Isn't automation wonderful?  It solves all our problems...

They should have an automated message that says "State your location" or something along those lines and you either say "North Florida" or "South Florida" depending on your location. I haven't had any issues with my MA phone number in contacting FSS in FL.


text:
INOP parking brake on checkride
The ACS states that the applicant must secure the airplane and complete the appropriate checklist.  The checklist states to set the parking brake.
But what if the parking brake is inoperative?  What would be the appropriate action for securing the airplane on the checkride?  Carefully get out while ensuring the plane won't roll, and insert chocks ASAP?
Thanks

You might impress the examiner with situational awareness and utilization of resources by asking to hold the brakes while the plane is chocked and tied.


text:
Phone number for FSS besides 1800wxbrief
Are there other "local" phone numbers to reach FSS besides 1800wxbrief?
The answer seems to be "yes," but does anyone know where to find them?
Thanks

if you search for FSS numbers in Alaska, you can find them on the FAA's website link Page 10

Alaska is unique in continuing to offer local Flight Service Stations.  In the lower 48 states, weather stations have been automated and FSS functions have all been consolidated into a single call-center location.
So to answer your question, there are no "local" flight service stations any more in the lower 48.  You can find more background information by doing a word search on "consolidation of flight service stations."

In the first paragraph you say that Alaska has local Flight Service Stations and in the second paragraph you say there are no more local Flight Service Stations.

I added "lower 48" to the second paragaph for clarity.

What about Hawaii?

@Someone, good question, not sure.  If I have time to research further I will modify my answer...


text:
Are FAA Written Exam Questions 'Dynamically' Selected?
I tried to google this and could not find the answer.
For the FAA written exams (private pilot exam, more specifically), how are the 60 questions selected?
I have heard it said that they are dynamically selected as you go, and if you get something wrong, you will be given more questions related to the ones you get wrong.
Does anyone know if this is true?  Or are all the questions selected before you begin, and those are the ones you'll answer no matter what you get wrong?
Thanks.

Where did your hear this?

No, the questions are not dynamically selected. All of the questions are available at the start of the exam and you can skip around in the testing software to each question at any time.
If you use test prep software like Gleim and others, they have a "test emulation mode" which is very similar to the actual test environment, and you can see how it works. In the screenshot below, you can see that there is a drop-down menu where you can select any question you want to skip to.

Source: I've taken knowledge tests for Private, Instrument, Commercial, Fundamentals of Instruction, Advanced Ground Instructor, and Flight Instructor exams. They all worked the same way. They present you with number of questions relevant for the exam, accessible through a drop-down menu. I've taken the tests from CATS, LaserGrade, and PSI. The test environment was similar in all of them, although PSI is the only test provider left, I believe.


text:
What is the meaning of "Bulk Strip"?
What does the following mean and what ramifications does it have when purchasing an aircraft?

term R/H-1958 HOURS SMOH@26/02/1988   - BULK STRIP 27/03/1998  ENGINE
  1472 SMOH

Does it mean the engine will be at its lide use and has to be replaced with another or am I correct that they replaced some parts to extend the time based on condition and will require a full overhaul 528 hors?

Related question about overhaul terminology

A bulk strip may be an Australian term, e.g. this airworthiness bulletin and this engine shop. I'd never heard of it before, but looking at those sites it seems to be something like a limited overhaul. The AB and the engine shop both list the steps and they're more or less the same: disassemble the engine, inspect all parts, replace any parts that need replacement, reassemble and test the engine.
I'm not an expert on maintenance by any means, but it looks to me like the difference between a bulk strip and a full overhaul is that the bulk strip is precautionary or diagnostic, as suggested by the machine shop site:

Not all engines need a full overhaul. You may have had a prop-strike,
  or your LAME may have identified metal in the filter or a crack in the
  crankcase. The pilot may have noticed unusual running of the engine.
We can ‘bulk-strip’ your engine for a full diagnosis and provide you
  with a report of your engine’s health:

Looking at it another way, an overhaul will replace a lot of parts whether they need it or not; a bulk strip may replace parts if they're worn or broken.

This is consistent with this question on PPRuNE.


text:
Is there a such thing as an ARINC label for the yaw angle?
Is there a way to check the yaw angle on the ARINC bus? If so, what is the associated ARINC-429 label?

Non-authoritative list of some labels:

ARINC 429 Labels

But labels are not all defined in ARINC standard, a specific LRU can define custom values. So you need to get label list from LRU documentation. For instance, labels used by Laseref VI IRS to output values to the bus are:

Source: Honeywell
Your question is ambiguous about what you are looking for: Yaw is the rotation around an axis normal to the plan defined by longitudinal and pitch axes. The origin can be multiple:

It can be seen absolute, for instance referenced to the north, and it would be the heading. It can defined relatively to a given direction, e.g. the wind, and it would be computed from other values. More likely it can be a rate.
Here are some related labels:

Yaw rate = 330
Heading: True = 314, Mag = 320
Track angle: True = 313, Mag = 317
Wind direction: True = 316

(octal values)
Could you provide details about your needs?

The difference between heading and track is the wind drift angle, not the yaw.

I don't know the technical definition, but probably something like the difference between the heading and the relative wind.  If an aircraft has access to the yaw angle, it is typically from an accelerometer and not from other inputs.

The heading is the yaw angle.

Actually, it depends on what he is looking for.  Since an aircraft has a yaw axis, that could translate to the heading as DeltaLima points out. An aircraft can also perform the action knows at yawing, which is actually a rate of change in the heading, but as pilot's we typically refer to a yaw as the uncoordinated maneuver that can be obtained by simply pushing the rudder. In short, it's somewhat ambiguous...

I apologize for the lack of detail, thank you for this. I do realize the LRU manufacturer is at liberty to define what the labels actually mean, it's just that sometimes they don't tell you.

Does this post fully answer your question?

authors: Δημήτρης Μποζίκης


text:
Where does the lift act on a B747-400 wing when the aircraft flies straight and level?
I'm doing a math exercise and I'd like to understand:

Where does lift act overall on the wing of a B747-400 when the aircraft flies straight and level at its cruise speed.
Which parameters, if any, may significantly affect the location of this point.

I'd appreciate if you share a reference document.

For almost any simulation (short of an advanced fluid dynamics simulator), wing lift is centered at the thickest part of the wing, which is where the 1st derivative of the upper-edge is 0.

The angle of attack does not have anything to do with the horizon; it is 0 when the angle of the wing chord is equal to the angle of the wind passing the wing

Related: http://aviation.stackexchange.com/questions/16193/how-do-wings-generate-lift

Welcome! I'll edit your question so that it doesn't attract downvotes, it you are unsatisfied with the adjustments you can always restore your version (rollback) using the edited... link at the end.

Thanks for the response, but I need some sort of a reference document. Otherwise, i cannot use the information. Thanks!

Getting closer to the transonic regime modifies the application point.

I am sorry, but i have no idea what that means. Could you dumb it down and explain?


text:
How can I find out if a close encounter in flight would be classed as an airprox?
I was on a Jet2 flight LS257 which left Leeds Bradford (LBA) at 06.30 on Sunday the 11th of September 2016.
Approximately one hour and ten minutes into the flight we passed very close to a Ryanair jet going in the opposite direction. I know that distances can be deceptive but this was much nearer than any time I have ever seen in the past. I often watch for other planes and have seen them countless times at varying heights and going in all directions but this was extremely close in my opinion.
Is there a way to check how close the two aircraft were?

RVSM can have 2 airplanes pass, one directly over the other, only 1,000 feet (300m) apart.   That can look very close, but its controlled and completely safe.  Also, there is no formal definition or classification for a "near miss", that is a vernacular term.

And to put what @abelenky said into perspective, the distance would be about 4 to 6 plane lengths or 5 to 7 wingspans apart.

It's possible that the pilot saw it as a non-event because of how close you can get in RVSM airspace and just didn't commit it to memory. I wouldn't take him saying he didn't notice it or "it was miles away" as a conspiracy, it was probably routine.

And finally, your question is, "Did he deny it so that I wouldn't worry about it?", which is not a question we can answer.

Related

@mins Generally separation must be either vertical or horizontal; so, separation in RVSM between FL290 and FL410 must be either 1000 ft vertically or the applicable horizontal separation.

@JonathanWalters: That makes sense (now that I think again, actually it would be difficult to maintain both in holdings).

No definition for "near miss", but one for "airprox". So I'll edit the question title. Still air-miss can be seen is professional publications: "Airprox investigations and similar studies into near-miss incidents focus on the risk to passengers and crew". And "near mid-air collision" is defined in the US.

I've finally identified the flight you most likely saw out of the window. There was an oddity with Fligtradar24 where the data was missing for the flight, but I've straightened out that mystery.
First for the Flightradar24 oddity:
You were on B757 registration G-LSAE on from LBA to PMI. The previous flight that aircraft had taken was LS444/EXS4CX from HER to LBA. For some reason when your flight left LBA it was still showing on FR24 as LS444/EXS4CX. After it crossed into France over Le Havre it changed to showing as LS831/EXS81WF which is usually a flight from MAN to PMI. I can't explain this, but the registration, time and route matches exactly with the routing shown for LS257 on FlightAware, so this is your aircraft.
Now for the flight you saw:
There were only two RyanAir flights that you crossed paths with that might have been close enough to see. FR6462/RYR88FJ passed about 15-20 miles from you. But at 6:39 UTC over Lunay, a RyanAir B737, flight FR9052/RYR43EZ passed very close. I'm sure this is the aircraft you saw. According to the data, your aircraft was at 35,000 feet on a heading of 164° feet and the RyanAir was at 36,000 feet on a 12° heading. So, although the lateral separation was very close, the standard vertical separation of 1,000 feet was maintained.


text:
Do tufts show boundary layer flow or outer flow?
Outer flow and boundary flow are often different.
Do tufts at the wing surface show boundary layer flow or outer flow?
Picture source.

Paint shows boundary layer flow.
Picture source

It does show boundary layer flow, that's why it can indicate when the flow is seperated. also, these things stick right to the surface - they physically cannot show the "outer flow". (to show outer flow, they will have to be placed a few centimetres away from the surface.)

@AdityaSharma Please post answers as Answers, and not as Comments.

@RalphJ In my opinion, it was not fit for an answer, so I posted it as a comment.

If you really want to understand this topic, read Doug McLean Understanding Aerodynamics: Arguing from the Real Physics. This book will answer your question and just about any other question you can think of, including how to interpret flowviz and the differences between streaklines and flow outside the boundary layer.

The boundary layer being the layer of flow with less velocity than the free stream, and which can be from nearly zero at a leading edge to an inch or two thick at a trailing edge, you can say that tufts are generally showing boundary layer flow except on or near leading edges where the flow is laminar and the boundary layer is so thin, the thickness of the tuft may put part of it in the free stream.
But as soon as the laminar part of the boundary layer ends and the boundary layer is thicker than the tuft itself, the tuft is pretty much immersed in the turbulent boundary layer. As you go farther aft where the turbulent boundary layer gets thicker and thicker, the tufts may lift off the surface a little bit, hinting at the increased thickness of the BL but not indicating how thick it actually is.

"part of it in the free stream" not exactly free stream - free stream flow is one that is unaffected by the presence of the aircraft. The flow that you are talking about is affected by aircraft's presence, just that it's not affected by the viscosity effects. Perhaps that's why the questioner used the term "outer flow". Also, boundary layer is not "flow with less velocity than free stream" - a more appropriate definition would be "flow affected by the viscosity effects".

But at a leading edge where the flow is laminar the boundary layer can get down to .020" or so, and a tuft stuck there that is a piece of 1/16th inch yarn will be technically partly in the free stream.

It will be out of the boundary layer, but not in free stream. The laminar, out of the boundary layer flow at the leading edge still cannot be considered "free stream" because it is affected by the presence of the wing (it is affected not by the viscosity effects, but by the pressure effects - it does not have the same static pressure, dynamic pressure and vector [of dynamic pressure] as it would in the absence of the wing).

I'd also use the term "outer flow" instead of "freestream". Freestream is the flow free, i.e. not modified by the the presence of the aircraft.

@JohnK Paint and tufts show same airflow pattern?

Freestream is just the flow not slowed down by surface friction. If you go by that definition, you have to go half a wing span away or more before you're in undisturbed air.

@user207141 Paint shows the boundary layer up to the thickness of the paint. A tuft is just thicker. They're both being carried along by the airstream they're in, except one is anchored to the surface.

@JohnK: by definition freestream is the flow not modified by the presence of the aircraft, i.e. the stream very far from the aircraft.

@sophit I can see that as a literal definition, but for practical purposes it's referred to as everything outside the boundary layer. Pitot probes mounted 3 inches from the surface are considered to be in the freestream flow, even though they are in air affected by the movement of the body.

@JohnK: I perfectly understand your point but confusing terminology doesn't help in a site like this one. And pitot tubes are not in the freestream, that's why they need to be calibrated according to where they are placed on the fuselage. The only pitot tube lying in the freestream that I can think about is this one.

I can't find any definitions of boundary layer that don't consider all of the flow beyond it "free stream velocity" that assumes no difference in velocity between flow adjacent to the boundary layer vs flow 50 ft away, although there may in fact be differences for obvious reasons. For the purpose if discussing and defining boundary layer, I don't think that distinction is considered important.

@JohnK At the low pressure peak on the wing's upper surface, the flow is faster than freestream - it cannot be considered free stream. Behind the wing, the flow is down-washed - it cannot be considered freestream. Ahead of the wing, the flow is up-washed - it as well cannot be considered freestream, but for the purposes of measuring the pitot pressure, this location can be used, since placing the pitot tube here gives a reasonably accurate data. However, I do agree with you that distinction is not important in this case; I was just pointing out that distinction does exist. Good day!

Comments after @JohnK's answer prompt an observation: it depends on the Angle of Attack.
The whole point of having "tufts" in research is to explore areas in the flight envelope where we don't have these nice neat definitions of airflow properties.
Airflow by any name creates lower pressure over the top of the wing by constantly "wicking" air away from the surface (Coanda effect).
This "vacuum pump" only works if air is taken away at an equal or faster rate than it can leak back in.
So we have a flow velocity gradient and a pressure gradient as one moves away from the wing surface which maintains the lifting force.
As John mentioned, the boundary layer thickens and becomes more turbulent towards the rear of the wing. Tufts can show this by "wiggling" a bit, but by maintaining their rearward orientation, they are showing the velocity gradient is still intact.
At stall, the pressure gradient breaks down and wing surface airflow becomes chaotic and/or reversed.  What better way to show this than with a tuft flopping all over the place.


text:
Top loading an aircraft vs bottom loading
When an aircraft carries a load, it could be mounted on top:

This is the Myasishchev M-4 carrying the Energia rocket fuel tank.

This is the American side.
Other times it could be mounted below:

My questions is:
What determines the reason where to mount the payload?
Attempt to answer:
The initial thought is, it might be easier to mount a large payload on an aircraft on top, which does not have a purpose built ground clearance. There simply may not be enough space under the aircraft.
Another reason (a concern for the FA/18) is that the ordnance mounted on the hard points generally will have gravity applying a tensile force on them, and when the aircraft is accelerating against gravity, the total force will increase on the mount point.
A top mounted load, in contrast, will lead to a compressive force in this situation.
Tensile force often might lead to a failure of the hard points faster than a compressive force. All ordnance have a maximum allowed G-limit. (Aircraft accelerating in any other direction where gravity is normal to it will not have to worry about gravity summing up to change the total compressive/tensile force.)
What I am left wondering is, are there other (aerodynamics or control/stability related) reasons, why a load may be mounted on top or to the bottom of the aircraft? How does the answer change for low, slow flying UAV?
I saw this post on reddit, and it talks about bringing the prop plane closer to the horizontal plane where COG is for quadcopters. What are the general principles?
Please also point me to books or resources.

I'm not sure you picked the best examples. The first two examples are existing planes that were modified to carry a ridiculously sized load, so there was simply no space to put the load anywhere else than on top. The third example has a drop tank, which is supposed to be … dropped … so it has to be on the underside. The same applies to bombs. Also, the weapons are installed and armed by ground crew, so need to be within arm's reach. Compare to the Roc, White Knight Two

… or White Knight, which were purpose-built to carry a heavy rocket underneath their wings. (But then again, they are not transporters, they are air-launch platforms, so they have the additional constraint of not only carrying but also launching their payload, which is done easiest by dropping it, which requires mounting underneath.)

@JörgWMittag , THat is why, i mentioned : The initial thought is, it might be easier to mount a large payload on an aircraft on top, which does not have a purpose built ground clearance. There simply may not be enough space under the aircraft.
But I am asking if there are other reasons.

That's an answer @JörgWMittag.

@JörgWMittag: please post it as an answer since it is

@mins that is what i am really looking forward to read. please point me to the right direction

With regards to stability & control, reference "keel effect", "pendulum stability."

Both are less ideal than carrying the load internally, so truly purpose will drive the decision.

"Size" I'd say ;-) Imagine loading the tank in the first photo below... Also: Bombs on top of the aircraft could be tricky when they fall down.

Maybe more support was provided than is clear in the photo, or maybe more support was added later, but that Myasishchev M-4 looks like a disaster waiting to happen.

@AeroAndy depends where the vertical CG is, rate of roll, and the effectiveness of control surfaces.  In pre-computer days, the pilot(s) would have to be alert.

You may be overthinking this @Sean  . In your first two examples it would not fit underneath.  So there's no other option.  That's all there is here?

The payload is mounted on the bottom if possible for improved stability and ease of attaching.
The pendulum effect doesn't apply in a coordinated turn. But roll without turning with a heavy top mounted payload will increase unless countered. This isn't desirable even for jet fighters - they prefer "relaxed stability", which is basically instability, without strong stabilizing or destabilizing forces in absence of pilot input.
Underwing weapons on jets are basically mounted on the centerline. Unless loaded with large gravity bombs, a fighter retains broadly similar control response between different AoA loadouts. For any detachable load (combat or not), bottom mounting allows for gravity release, which is a massive safety improvement.
Underslung payloads, often used by helicopters, don't create stability or instability per se, but in practice they can do both, slowing down the maneuvers or creating instability through pendulum motion (unrelated to the pendulum effect).
For a cargo plane, bottom-mounting the payload is always safer for most purposes, but only if there's room for it, which is usually not the case. Top-mounting does work, but it does reduces your margins of error.

Isn't it true that aircraft don't experience the pendulum effect? Meaning that having weight below the CoG doesn't make the aircraft more stable, and conversely having the payload above the aircraft doesn't cause instability? I read that from here, but it's very possible I'm misunderstanding.

@Wyatt The pendulum effect doesn't apply to high or low wing placement. But stability is affected if you take a plane that's balanced as is, and add a big load to it.

As mentioned elsewhere, you could add that weapons fall immediately after deployment with bombs continuing to fall and missiles igniting after a brief fall. Bombs simply could not be mounted above and missiles only if on rails (e.g., AIM-9), but having rails for missiles makes mount points inflexible - upper mount points could only take missiles which would prevent mission flexibility. Also mentioned elsewhere is mount point accessibility for ground crew. I know the question specifies aerodynamic reasons, but other factors can override aerodynamics.

Adding to @ToddWilcox 's comments another users.  Access to the mounting points.  Large loads like that external fuel tank or the shuttle were loaded with overhead cranes.  They are specialty cases not performed every day.  Calling in a mobile crane to place the load is something you plan a long time ahead for.  Bombs, missiles, drop tanks etc are something that may be added multiple times a day.  There is specialize lifting equipment for this that only has to make the attached item travel a very short distance.  You will have multiple lifting devices ready to prep a plane or squadron. cont

Where as you will only have one or two special lift cranes for the entire large item loading case.  Size permitting you could also load your cargo internally using the Antonov (RIP), C5 Galaxy, or even NASA's Guppy.

A couple of things. The Soviet aircraft above transporting the fuel tank or NASA’s 905 SCA 747 are examples of how to use existing aircraft to move physically large or awkwardly shaped payloads that will not fit inside of the internal cargo space of existing aircraft. In this case a “piggy pack” configuration works well. The disadvantages to this is that it produces a lot of parasite drag as well as causes lateral and yaw stability problems, generally addressed with larger tail surfaces.
Some aircraft are designed specifically for oversize loads. These include Airbus’ Beluga conversion of the A300 airframe, the Boeing DreamLifter 747-400 conversion and the Aero Spacelines Super Guppy modified from a Boeing 377 StratoCruiser airliner.  The specialty airplanes have been used to transport fuselage sections from other aircraft and even rocket boosters and individual stages of space rockets and ballistic missiles.
Large cargo aircraft can carry standard size pallets and shipping containers in their interior. They can even accommodate small vehicles or other aircraft. The Lockheed F-117 Nighthawk was designed such that its wings could be easily removed, and the fuselage and wing set loaded into a Lockheed C-5 cargo aircraft for transport.  Said cargo aircraft can also be used to paradrop large pallets of equipment or even vehicles out of their rear ramp.  Some very large munitions such as the Vietnam era BLU-82 ‘Daisy Cutter’ or GBU-43/B Massive Ordnance Air Burst (MOAB) launch that way from the C-130 cargo aircraft aboard specially designed sleds which separate for the munition once clear of the aircraft.
For smaller combat aircraft and underslung external payload for fuel tanks and ordnance works well, provided the payload can be centered very close to the aircraft CG.  This  is one of the reasons that most weapons hard points are located on the wings of an aircraft as well as waist and centerline stations.
Underslung payloads also facilitate ease of loading, unloading, or reloading ordnance during combat operations not to mention making it much easier to release freefall weapons such as bombs.  There have been some rare cases where combat aircraft have used overslung weapons. The SEPECAT Jaguar, for instance, had overwing missile rails for Sidewinders.  I suspect this was done to free up more real estate on the bottom side of the wing for air to ground ordnance.
Externally mounted payloads or weapons also have a consequence of vastly increasing an airplane’s radar cross-section, which is why current low observable designs are opting for stores carriage inside internal weapons bays.  This both preserves the aircraft’s stealth signature as well as reducing parasite drag.

You have random commas in several places that make this hard to read, e.g. "combat, aircraft".  And "airplane's, radar cross-section".

Yes, I have a tendency to dictate my answers and Apple speech recognition is not very good at picking up on what a sentence structure should be.

As the person who would be loading/reloading/unloading those munitions, I can say without reservation that overwing hardpoints would increase the complexity, manpower, and time required. A LOT.

If the load is meant to be released during flight, hanging it below the airplane is much preferred to ease separation. Bombs, fuel tanks and missiles are almost always mounted below, with the notable exception of the overwing tanks of the EE Lightning or the short-range air-to-air missiles of the SEPECAT Jaguar (pictured below, source).

This position was chosen because all other places were already taken, and a missile will separate more easily than a bomb (which is visible hangng below the wing in the photo above). If you want to learn what could possibly go wrong when releasing something in flight, watch this video.
The next reason, of course, is the much easier replenishment of those underwing or underbelly positions. Only when the load becomes too large for hanging it below the airplane will it be mounted on top.
For the Me-109 even a jettisonable auxiliary wheel was tested to allow take-off with a 1000 kg bomb which would not have fitted between fuselage and ground without raising the tail by means of that extra wheel (picture below, souce). After take-off the wheel simply fell off and landed hanging on a small parachute.

Also, the underwing position has aerodynamic benefits: Since airspeed above the wing is higher than below when lift is created, a body stored below the wing produces slightly less drag than one above. Ease of separation can also be added to the aerodynamic realm since releasing an overwing load needs plenty of angle of attack on that load right after release so lift will carry it up and away from the airplane. For an underwing load, some nose-down attitude is helpful, but weight will already help with separation. In total, however, aerodynamic considerations have much less weight when selecting a storage position.
The kind of stress in the hard points is even less of a factor.
In terms of flight mechanics, the lengthwise position is much more important than the vertical position. Since most external payloads behave like slender bodies, they are destabilizing the airplane. They cannot be mounted too far aft in order to keep the center of gravity in the desired range, so this destabilizing effect must be compensated either by oversizing the vertical tail from the start, or by adding auxiliary vertical surfaces at the tail later.
Paul Allen's Stratolaunch uses a raised profile at mid-fuselage to allow a high enough wing position such that the massive booster it is to carry will fit below. The B-52 from which the X-15 was launched even accepted a wing cutout to make an underwing position possible.
Only when a payload is sure to stay attached until landing will an overwing position even be considered. The Ju-87 could be fitted with overwing pods to ease the relocation of personnel to a new base (picture below, source). For that purpose the position on top of the wing made more sense.

One can notice that the CG of the Ju-87 is raised significantly without the bomb, hence the higher side area of the pods matches.

The overwing passenger pods led me down a delightful path - similar pods were evaluated for parachute-dropping spies or saboteurs plus their equipment.  For water landings, the pod included an outboard motor.  For hard landings, retro-rockets(!).

Loading considerations are as follows:  relation of center of thrust to center of drag (front), sideslip force to vertical center of gravity, and relationship of added weight to existing center of gravity.
Last first, obviously the center of mass of the added structure should be placed at or near the existing center of gravity (near the center of lift).
If possible, try to avoid excessive trimming by having the new center of drag (forward) as close to the original one as possible.  The farther above or below the center of thrust it is, the more trimming will be required when changing airspeed.
The side slip forces can be a bit more detailed, as the object being transported on the M-4 will raise both the center of gravity and the center of (sideslip) drag!
Judging by the modified vertical stabilizers$^1$, the Energia tank raised the center of drag slightly more.
Finally, the consideration of attaching cargo above or below the wing (if ground clearance allows) would be favoring below the wing as lift production is less affected.  This is because lift below the wing is more from a simple ram effect of a surface at an angle of attack to the relative wind, causing an increase in pressure, whereas lift production from the upper wing surface works best with undisturbed airflow.
$^1$ similar to the Heinkel 162

You didn't address the overwing or underwing aspect at the root of this question.

I rather read placing the load on top or underneath the entire aircraft, keeping in mind it still has to be flyable (safely).

Yes, and your answer doesn't touch this.

Folks, if you haven't built a balsa glider and tested it in a crosswind, all this may be difficult.  It helps to consider the aircraft and the load one unit, and work from there to make it a stable and safe aircraft to fly.

Indeed, but that doesn't address the question...

... and we finally get to an acknowledgement of the actual question. Now simply explain why that is and I might flip my DV to an upvote!  ;)

Because the lift under the wing is based on slower air and higher pressure (hanging ordnance does not affect this nearly as much) as compared with lift created by airflow over the upper wing, creating lower pressure.

So, are you going to answer in comments here, or edit your actual answer?!


text:
How to carry out a CFD simulation for determining the stability derivatives of an aeroplane?
I want to create a 3D model of an aircraft to determine the stability derivatives by using a computational fluid dynamics (CFD) simulation. I tried to google for tutorials that explain how it is possible to carry out a CFD simulation for determining the stability derivatives of an aeroplane but was not successful. I would be glad if someone could give some resources that explain the procedure. It would be great if the CFD software would be ANSYS Fluent.

Make a list of the derivatives you want to determine. All of them will be derivations of some force or moment with respect to some parameter or control setting. Now set up your CFD such that you get lift, side force and drag as well as pitching, rolling and yawing moment relative to the center of gravity.
Next, make those forces and moments dimensionless. Forces are divided by a reference area (projection of the wing area in most cases) and the dynamic pressure (speed squared times air density divided by 2). Moments are in addition divided by a reference length (span or semi-span for rolling and yawing moment, mean wing chord for pitching moment). The results are called coefficients. Record those coefficients for a baseline configuration (say, level flight at cruise speed).
Now make a small change in the parameter (angle of attack or sideslip, speed, air density, pitch-, roll- or yaw-rate) or control setting (elevator, rudder or aileron angle, flap setting, power setting) and record the coefficients again. Only one change at a time and leave all others at their baseline position! The desired derivative is simply the gradient of the coefficient over the gradient of the parameter, as in
$$c_{M\alpha} = \frac{c_{M1}-c_{M0}}{\alpha_1-\alpha_0}$$
with 0 denoting your baseline figures and 1 the changed ones. Use radians for all angles. The rotation rates you should make dimensionless by dividing the value by the flight speed and multiplying it with the respective reference length. And another thing: The really correct reference length for the pitching moment and -rate is the mean aerodynamic chord which is the integral of chord squared over span, divided by wing area.

To do this manually, carry out a tremendous amount of bookkeeping and use books about pre-desing of aeroplanes, such as my goto book of Torenbeek.
To let a computer program compute the stability derivatives: Openvsp.org consists of a vehicle sketcher and a couple of programs that do computation of wakes, lift, drag, moments etc. Originally developed by NASA and now under open license.
Procedure: sketch your vehicle and use vspaero for computing the coefficients. The sketch configuration can be exported to formats suitable for pure CFD.


text:
What is this part on the Me 262?
I have seen this part on a me 262 model kit but I don't know what it is... I've make some research on it but I find nothing! Maybe it can be radar, or a weapon? Do you know what is this? And also its function?

They are Werfer-Granate 21 rocket launchers -

The Werfer-Granate 21 rocket launcher, also known as the BR 21 (the
"BR" standing for Bordrakete) in official Luftwaffe manuals, was a
weapon used by the German Luftwaffe during World War II and was the
first on-board rocket placed into service by the Luftwaffe, first
introduced in mid 1943.

On the Me262 they were mounted one each side of the nosegear well.
This is the exact aircraft your model is based on -

Messerschmitt Me262A-1a 'Green 3' of the Geschwaderstab [headquarters unit] of JG 7 prepared
to move off across the concrete surface at Brandenburg-Briest in
February or early March 1945. The aircraft, finished in a relatively
rare application of streaked horizontal lines, has been fitted with a
pair of 21cm WGr air-to-air mortar tubes visible beneath the fuselage
aft of the nose wheel. (source)


text:
Why are APU engine generators rated in kVA and not kW?
Auxiliary Power Unit (APU) generators seem to be rated in kilo-volts-amperes (kVA) and not kilo-watts (kW). Are kVA not the same as kW? Is there a reason why the generator is rated in terms of kVA instead of kW?

A Volt-Ampere is the same thing as a Watt, just a different way to express the quantity.

@JonathanWalters No, they're not. VA is apparent power, watts are real power.

@SomeoneSomewhere Let me clarify that for DC circuits the product of Volts times Amperes is the same as the real power in Watts. However, if the generator is rated in KVA, that may be an indication that it is an AC generator, not DC, in which case you are correct that KVA would not be strictly equivalent to KW.

@SomeoneSomewhere what is the difference between the two?

I'm pretty sure that APUs have three-phase generators, because they are stronger and their power output is constant over time. Even today's cars have three-phase alternators, though the entire car needs DC.

@antBldel (This is an oversimplification.) When you supply AC to a motor, power flows to the windings of the motor to build a magnetic field, but then when the magnetic field collapses, "unusued" power is returned to the source. Watts measure just the power used. kVA measures the flow. A motor that consumes 10kW might need a supply that can handle 15kW (with 5kW "ping ponging" between the supply and the load). So a 10kW generator may not be able to run a 10kW motor.

BTW, the kVA designation is used on all types of AC generators, not just on APUs.

Current and voltage don't always vary at the same time, one usually lags, this lag is the root of evils found in electrical engineering.
Any device is a mix of resistive load (no lag), inductive load (current lags) and capacitive load (voltage lags).
The lag (phase shift angle) is denoted with Greek letter φ, and usually expressed as cos φ, or power factor. Power factor $=100 \cos φ$. Each device has its own individual φ, which may vary with conditions.
Lag effect is only visible when voltage or current changes. This happens transiently in DC when the circuit is closed or opened (effect used to create high DC voltage from low DC voltage in a contact breaker), but constantly in AC  (not mentioning other induced variations, e.g. changes in mechanical demand on an electric engine will change the impedance of the coil, so the current). The effect of the phase angle increases with circuit frequency, and is significant in aircraft circuitry, with major loads working at 400 Hz.
With this lag, the voltage and current mean (RMS) values are not sufficient to size electrical circuits. A phase shift introduces additional power in the circuit. This reactive component is not described by the RMS values, it's only visible when looking at instantaneous values, for example on this animation of the addition of two phasors, where the fixed circle radii indicate the mean values, and the moving dots show the instantaneous values. In simple cases one can determine the power required using the triangle of powers:

(Triangle of powers, source)
The apparent power is the sum of the real part of the power (resistive load in W) and the imaginary part (reactive load in VAr).
Work (Joule) is only produced by active power (the reactive power produces no actual work) and the active power rating of the generator must be higher or equal to the active power rating of the load. However the reactive power produces a reaction on the generator (by phase shifting the current) and must be accounted for when sizing the generator. The generator must have an apparent power rating higher or equal to the apparent power rating of the load, at the working phase angle.
A higher apparent power, regardless of the active power, requires a more robust generator and wiring to prevent overload.
One way to simplify the required power calculation is to just add the apparent power value of all devices (in VA). The result in VA or a multiple like kVA is conservative. This allows to select the generator required, provided we know its VA rating too. This is why generator manufacturers provide this value.

Notes:

All units, VA, VAr, W, are of the same kind (dimension of power, W). VA and VAr denote the fact that voltage, current and power are not varying in-phase in AC circuits. These units describe the kind of "power" we are taking about.
When the apparent power rating (VA) is the only rating known for a device, the active power rating (W) can be assumed to be no more than 60%, however the actual value depends on multiple factors and this is only a quick approximation. A generator must be provided with a chart showing the relationship between VA and W under different conditions of use.
A generator cannot work under any power factor, and cannot maintain the same efficiency across the valid power factor range. It is provided with a table or graph showing the acceptable conditions. For example, for this generator, the power factor must be kept in the green area (inductive load, between 80 and 100%), and will start being unreliable at some power factor, depending on the active power delivered and the type of reactance (red area).

(Source)
The explanations above are really simplifications, because in AC, the phase difference is only one side of the problem of reactive power. The other side is the presence of harmonics which are per definition out of phase.

The general principle in electricity is that voltage is set by the generator, and current is set by the load. The load can set a current which has the same frequency than the voltage, this is what we assumed for the answer. However most of the time the load sets a current variation which doesn't coincide with the voltage frequency and/or shape.

This non-linearity between current and voltage creates 'harmonics' and unbalances phases (so a current start flowing in the neutral, which is not something we want).

A little story about that relates to first datacenters in years 1990. Standby generators (diesel) not well sized were unable to sustain computers loads, due to a capacitive reactive power created by computer switching power supplies (non linearity and a cos φ as low as 0.6) Fires ensued, it was time to understand how to deal with apparent power.
The $φ$ angle just comes from the general definition of a sine wave current. Current at time $t$ is defined by $a = a _{peak} \space sin \space (\omega t \space + \varphi)$ where $a _{peak}$ is the maximum current, $ω$ the angular frequency (314 rd/s for the EU grid) and $φ$ the phase shift angle.

Generators generally produce Alternating Current (AC).
Considering that the voltage is regulated, the demand on the generator determines the current, and the heat produced in the generator is directly related to the current, therefore the higher the current the higher the internal heating effect.
From the user's point of view, if the load is purely inductive (for example a solenoid) there is no consumed power, because the instantaneous taken energy is restored back to the supply immediately after, so the net consumed energy is zero while the generator is developing internal heat resulting from the current.
If the load is purely resistive, the delivered current is only producing heat and the produced kVA, as a calculated number, is equal to the delivered kW, as a number.
Since the generator is limited by the current it can deliver at a regulated voltage, it is normal to give the generator capacity in KVA.
To make the best use of the delivered KVA it is up to the user to reduce the induction in the load, for instance by addition of capacitors.
Of course this applies only to alternating current generation. For filtered DC generation, kVA or kW would mean the same,  because there is no way in DC generation for the user to restore back the instantaneously used energy.

I thought generators produce DC, alternators produce AC.

@Juan Jimenez, Generator is more general than alternator, but in APUs generators are likely alternators. More precisely:   In electricity generation, a generator is a device that converts motive power (mechanical energy) into electrical power for use in an external circuit.

@JuanJimenez A dynamo produces DC, an alternator AC, and both are generators.


text:
What are these symbols on the runway?
As just a passenger, not a pilot, this may be a very basic question, but when I am on an airplane leaving the terminal, it goes over a symbol on the tarmac that looks like this:

Also I see signs on the side of the runway pointing to those markers.
On a related note, there is a similar sign near the gate that looks like this:

What do these signs mean?

I was wondering if they had dark background (like the one I put in your question), or yellow background (this is another meaning).

I think I have seen both.

It is the line that you don't cross without ATC permission if you don't want to get butt-squashed or impaled by another airplane.

The first one is the holding position marking. It denotes the entrance from the taxiway into the runway. The dashed lines are in the side of the runway.

The second one is the non movement area boundary mainly for vehicles, which divides the movement and non-movement areas of boundary- the movement area is on the dashed line, for moving into which you'll need ATC clearance.

Images from FAA Guide to Ground Vehicle Operations

Doyou know if it coincides with the limits of ground ATC (simple lines) and tower ATC (double lines)?

@mins If you're talking about an active runway that's the case, but ground control generally handles the inactive runways, so it's not universally true. Basically it's a visual cue (in addition to the sign and the fact that the runway numbers are usually painted on the ground) to let you know that you're approaching a runway, and if you weren't expecting that you may not be where you think you are on the airport.

Here's the big book of everything:
http://www.faa.gov/air_traffic/publications/media/AIM_Basic_4-03-14.pdf
Your first example is a runway hold. That is the physical boundary of the runway.
See page 112 (PDF).
The second is a non-movement area boundary. This is the the boundary of where ATC controls. For example, they may park the snow plows beyond this boundary. When they plow crosses the boundary, it needs to be in radio contact with the ground controller in the tower.
See page 114.

As mins said in his comment, it's a "holding position" marking; it denotes the entrance to runway from a taxiway.  It's like the solid white line at a traffic light, except that pilots don't usually roll over it while waiting to be cleared onto the runway (waiting for the light to go green).
The sign you saw is a "Runway Safety Area / OFZ and Runway Approach Area Boundary".  It is on the side of a sign pilots will see when exiting an RSA (Runway Safety Area) or OFZ (Obstacle Free Zone).
Here's a reference of the various airport markings.

Because the OP isn't familiar with these markings, it might be helpful to expand your answer a bit to explain not just what they are, but also what they're for.


text:
Are aircraft accidents more frequent in specific countries?
In the past months I heard about several aircraft accidents that happened to occur in Russia, Indonesia, Malaysia... and I was wondering if some countries are actually more connected to accidents than other.
Is there some statistics on this topic? and if so, do they confirm this alleged over-representation, and do we know the reasons behind?

The Russians make fake airports and then put big rocks on the runways.

Because you are only watching very specific TV news, apparently ... have a look here: http://avherald.com/h?list=&opt=7680

thanks @J.Hougaard you are right, Probably it is because of spesific media companies.

@TylerDurden that was good buddy :)

Certainly some countries (and some aircraft operators within the same countries) don't have the same aviation safety standards as others, but aircraft crashes are hardly unique to Russia, Indonesia, and Malaysia. The most recent airliner crash to make international news was flying from France to Egypt, for example.

I don't agree that this is off topic; discussing aviation safety is certainly on topic. But it would be a much better question if it were more along the lines of this one, looking for specific evidence.

@fooot And yet almost no one is voting up my question as a good one :(

Crashes, meaning accidents with significant number of fatalities, are so rare, even in places with least attention to safety, that it is not possible to conclude the risk is higher in some countries with statistics.
And if you wanted to judge from the number of incidents, that is including events that were dangerous, but ended well, you would be stopped by the fact that quality of incident reporting varies wildly. In this interview Simon Hradecky, the editor of The Aviation Herald, explains that Canadian TSB reports many, many incidents, but that is is not because the safety would be poor in Canada – quite to the contrary – but because they have particularly good system of reporting them. So many incident reports can actually be taken as a sign of good safety in that country, but you can't make any statistics from that.
Regarding the countries you mention:

Indonesia is widely believed to have poor safety. The EU Air Safety List says:

All air carriers certified by
  the authorities with
  responsibility for regulatory
  oversight of Indonesia, with
  the exception of Garuda
  Indonesia, Airfast Indonesia,
  Ekspres Transportasi
  Antarbenua, Indonesia Air
  Asia, Citilink, Lion Air and
  Batik Air, including …

clearly indicating that EASA does not believe the aviation authority of Indonesia oversees operators registered under them sufficiently.
Together with high incidence of severe weather and a lot of mountainous terrain this creates environment where the risk might be elevated. As mentioned above, even there accidents are not that common to allow firm statistical conclusion.
The excepted airlines however proved to EASA that they have a safety management system in place and that it works according to industry best practice. With them, the risk probably isn't significantly higher than with any other decent airline.
Malaysia and Russia: I have not noticed any specific concerns about safety in those two countries. If you seem to have noticed accidents in those two countries in particular, it is likely just bad luck.

I don't have anything to back it up at the moment but I feel like there's something to be said about Malaysia and Russia. Maybe not as bad as Indonesia, but still.

@fooot, well, something can be said about Malaysia and Russia: Russia committed act of terrorism against Malaysia two years ago. But regarding accidents, for Malaysia I can only think about the missing MH370, which, while widely known, is a unique case that does not allow making any general conclusions. And for Russia the last bigger problem was the triple thrust reversers problem on Tu-204 that ended with crash on the last occurrence in 2012. Since then I recall 2 more crashes in Russia, but neither was Russian aircraft or crew. Nothing systemic in either.

@JanHudec I don't know about Russia now, but if you read about things during the Soviet period, especially regarding the space and nuclear industries, it's pretty clear that there was really no safety culture there. From appearances that appears to have changed, though.

@TomMcW, in many areas, the safety culture is still pretty poor there, but it seems that the aviation authority does do its job. Which is not commonplace; Russian government is still highly infested with corruption in general.

@JanHudec Was Soviet aviation better than other industries? Their nuclear energy industry had an awful safety record. They took way too many risks and important technical jobs were given on the basis of politics rather than qualifications. Read a book by a US bone marrow specialist that went there to help after Chernobyl. He related that their doctors were very familiar with radiation burns, suggesting they were fairly common. Radiation illnesses are exceedingly rare everywhere else. I really hope they've improved on such an unforgiving technology as nuclear power

@TomMcW, I suspect it actually, at least to an extent, indeed was always better. Covering up radiation accidents was relatively easy, but covering up aircraft crashes would have been a problem, especially crashes of their aircraft abroad. And they did always care about their image. So they did care about aviation safety, at least on the international lines, more than in other places.

i really appreciated for your answer and upvoted as a total beginner, but still i am pretty sure about lack of aviation for post-soviet countries.(well please do not judge me, i have travelled 42 countries and maybe 40 different companies but if i live that vibration of turkish airlines, quatar airlanes...etc. on landing i never buy ticket again but vibration and risk is more to be like felt for aeroflot,azal[azerbaijan airlines]..etc soviet ones, is clear) I do not want to emphasize spesific airlines of course, but the way is going to goal is starting from here! do you have any stat?

@abidinberkay, other post-soviet countries are a different story: Kazakhstan and Kyrgyzstan are on the EU Air Safety list. As I explained, I don't think reliable statistics is possible.


text:
What is the value allowed for runway transverse slope?
What is the range allowed for transverse slope for runways used by commercial aviation?

Which country? Which size of runway? Which pavement surface? I have flown into a lot of dirt or gravel strips on multiple continents that conformed to no limits whatsoever.

@mins Unless I am overlooking something the figures you quote are suggested ideal values, not intrinsic requirements, limits, or otherwise binding. I see the words should, if practicable, and ideally, but I do not see shall, must, or any other word indicating requirement. Any requirement or limit will likely be defined—even if only by reference to this document—in other agreements or contracts.

@JonathanWalters: ICAO recommendations must be followed by member states, or differences must be described in AIP. Correct? And as a matter of fact if we look at the US AIP GEN 1.7−83: "Minimum and maximum transverse runway slopes are based on aircraft approach categories as
follows: For categories A and B:  1.0 - 2.0 percent. C and D:  1.0 − 1.5 percent"

@mins The US has adopted the ICAO recommendations as regulation for certain airports serving certain scheduled air carrier traffic. The US also generally requires federally obligated airports to conform to the adopted recommendations, but by agreement, not by regulation. Many airports within the US do not conform.

modified question - What is the acceptable tolerance for a specified transverse slope on a runway???